Re: [Qemu-devel] [PATCH 04/13] qcrypto-luks: refactoring: simplify the math used for keyslot locations

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Aug 14, 2019 at 11:22:10PM +0300, Maxim Levitsky wrote:
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---
>  crypto/block-luks.c | 64 +++++++++++++++++++++++++++------------------
>  1 file changed, 38 insertions(+), 26 deletions(-)
> 
> diff --git a/crypto/block-luks.c b/crypto/block-luks.c
> index 6bb369f3b4..e1a4df94b7 100644
> --- a/crypto/block-luks.c
> +++ b/crypto/block-luks.c
> @@ -417,6 +417,33 @@ static int masterkeylen(QCryptoBlockLUKS *luks)
>  }
>  
>  
> +/*
> + * Returns number of sectors needed to store the key material
> + * given number of anti forensic stripes
> + */
> +static int splitkeylen_sectors(QCryptoBlockLUKS *luks, int stripes)

Needs a qcrypto_block_luks_ prefix on method name.

I'd also put 'static int' on a separate line from method name
to reduce too long lines.

> +
> +{
> +    /*
> +     * This calculation doesn't match that shown in the spec,
> +     * but instead follows the cryptsetup implementation.
> +     */
> +
> +    size_t header_sectors = QCRYPTO_BLOCK_LUKS_KEY_SLOT_OFFSET /
> +                     QCRYPTO_BLOCK_LUKS_SECTOR_SIZE;

Following line indent should only be 4 spaces

> +
> +    size_t splitkeylen = masterkeylen(luks) * stripes;
> +
> +    /* First align the key material size to block size*/
> +    size_t splitkeylen_sectors =
> +            DIV_ROUND_UP(splitkeylen, QCRYPTO_BLOCK_LUKS_SECTOR_SIZE);

Again 4 space indent.

> +
> +    /* Then also align the key material size to the size of the header */
> +    return ROUND_UP(splitkeylen_sectors, header_sectors);
> +}
> +
> +
> +
>  /*
>   * Stores the main LUKS header, taking care of endianess
>   */
> @@ -1169,7 +1196,7 @@ qcrypto_block_luks_create(QCryptoBlock *block,
>      QCryptoBlockCreateOptionsLUKS luks_opts;
>      Error *local_err = NULL;
>      uint8_t *masterkey = NULL;
> -    size_t splitkeylen = 0;
> +    size_t next_sector;
>      size_t i;
>      char *password;
>      const char *cipher_alg;
> @@ -1388,23 +1415,16 @@ qcrypto_block_luks_create(QCryptoBlock *block,
>          goto error;
>      }
>  
> +    /* start with the sector that follows the header*/
> +    next_sector = QCRYPTO_BLOCK_LUKS_KEY_SLOT_OFFSET /
> +                  QCRYPTO_BLOCK_LUKS_SECTOR_SIZE;

I'd suggest 'post_header_sector'

>  
> -    /* Although LUKS has multiple key slots, we're just going
> -     * to use the first key slot */
> -    splitkeylen = luks->header.key_bytes * QCRYPTO_BLOCK_LUKS_STRIPES;
>      for (i = 0; i < QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS; i++) {
> -        luks->header.key_slots[i].active = QCRYPTO_BLOCK_LUKS_KEY_SLOT_DISABLED;
> -        luks->header.key_slots[i].stripes = QCRYPTO_BLOCK_LUKS_STRIPES;
> -
> -        /* This calculation doesn't match that shown in the spec,
> -         * but instead follows the cryptsetup implementation.
> -         */
> -        luks->header.key_slots[i].key_offset =
> -            (QCRYPTO_BLOCK_LUKS_KEY_SLOT_OFFSET /
> -             QCRYPTO_BLOCK_LUKS_SECTOR_SIZE) +
> -            (ROUND_UP(DIV_ROUND_UP(splitkeylen, QCRYPTO_BLOCK_LUKS_SECTOR_SIZE),
> -                      (QCRYPTO_BLOCK_LUKS_KEY_SLOT_OFFSET /
> -                       QCRYPTO_BLOCK_LUKS_SECTOR_SIZE)) * i);
> +        QCryptoBlockLUKSKeySlot *slot = &luks->header.key_slots[i];
> +        slot->active = QCRYPTO_BLOCK_LUKS_KEY_SLOT_DISABLED;
> +        slot->key_offset = next_sector;
> +        slot->stripes = QCRYPTO_BLOCK_LUKS_STRIPES;
> +        next_sector += splitkeylen_sectors(luks, QCRYPTO_BLOCK_LUKS_STRIPES);

I'm not a fan of the next_sector accumulator .

I'd prefer to see the '* i' part done in splitkeylen_sectors, so that
we have

  slot->key_offset = post_header_sector +
        splitkeylen_sectors(luks, QCRYPTO_BLOCK_LUKS_STRIPES, i);

> @@ -1412,17 +1432,9 @@ qcrypto_block_luks_create(QCryptoBlock *block,
>       * slot headers, rounded up to the nearest sector, combined with
>       * the size of each master key material region, also rounded up
>       * to the nearest sector */
> -    luks->header.payload_offset =
> -        (QCRYPTO_BLOCK_LUKS_KEY_SLOT_OFFSET /
> -         QCRYPTO_BLOCK_LUKS_SECTOR_SIZE) +
> -        (ROUND_UP(DIV_ROUND_UP(splitkeylen, QCRYPTO_BLOCK_LUKS_SECTOR_SIZE),
> -                  (QCRYPTO_BLOCK_LUKS_KEY_SLOT_OFFSET /
> -                   QCRYPTO_BLOCK_LUKS_SECTOR_SIZE)) *
> -         QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS);
> -
> +    luks->header.payload_offset = next_sector;

  luks->header.payload_offset = post_header_sector +
        splitkeylen_sectors(luks, QCRYPTO_BLOCK_LUKS_STRIPES,
	                    QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS);


>      block->sector_size = QCRYPTO_BLOCK_LUKS_SECTOR_SIZE;
> -    block->payload_offset = luks->header.payload_offset *
> -        block->sector_size;
> +    block->payload_offset = luks->header.payload_offset * block->sector_size;


This is reverting a whitspace change done in previous method

Regards,
Daniel
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